I think people need to remember that Nintendo Directs are not just for Nintendo anymore. If a Direct isn't gonna happen until March then that would mean it's been nearly (or maybe even over) half a year since the last Direct, and for third parties who want that Direct buzz such a wait might simply be too late.
Also right now the only major third party games that are upcoming for the Switch are ones that were announced ages ago (Doom, Gods & Monsters, Deadly Premonition 2, etc) or ones published by THQ Nordic which historically doesn't appear in Directs all that much (Metro, Saints Row IV). For most of the major publishers there really isn't anything big on the horizon which definitely points to there being a potentially large number of 3rd party titles that are waiting for a Direct to be annonuced.